CHAPTER 3 . Coastal Lagoons of Southeastern Brazil
59
calculated by Pick's first law from pore water collected using the in situ "Peeper" sampling technique (Fernex et al. 1992) and applying standard temperature-corrected
diffusion coefficients. The results reflect seasonal variability of benthic nutrient fluxes,
with the highest flux usually occurring during the summer when the primary production is enhanced. Assuming the Redfield ratio to establish the nutrient demand by
phytoplankton primary production, the benthic supply of ammonia and orthophosphate sustains 10-30% of the primary production in the phytoplankton-based coastal
lagoons on both a seasonal and annual basis. In the case of Araruama 1., however,
the microphytobenthos-based primary production was entirely sustained by ammonia and orthophosphate release in winter. In late summer, ammonia was preferentially released over orthophosphate, which covered only 5% of the demand by phytoplankton.
Considering that the relation between sediment oxygen consumption and pelagic
primary production was 30-55% in the Brazilian lagoons, the pelagic compartment
regenerates a somewhat higher fraction of nutrients than the benthic compartment.
Some of the benthic oxygen consumption includes chemical oxygen demand, at least
for the oxidation of sulfide to sulfate. Most of the lagoon sediments are anoxic a few
centimetres below the surface.
3.14
Trophic State
The trophic state (TS), or degree of nourishment of coastal lagoons, is an indicator
that can be used to as a first step to assess the process of eutrophication and also to
develop management policies. There are many available methods for TS ranking
(Lambou et al. 1983).
The simplest measure of TS-ranking is the average annual stock, or peak value, of
chlorophyll a, total nitrogen (TN), and/or total phosphorous (TP). The choice depends
on which nutrient is limiting for primary production and thus should be selected (Rast
and Holland 1988). However, the extrapolation of the trophic state concept, which was
originally developed for phosphorous-limited temperate lakes (Vollenweider 1968;
Vollenweider and Kerekes 1982), presents problems when applied to nitrogen-limited,
tidally dominated estuaries (Rast and Holland 1988; Vollenweider 1992). For example,
using nitrogen as the TS indicator requires information on denitrification because it
has a compensatory effect on eutrophication (Golterman and Gude 1991).
Complications may arise in tropical coastal lagoons because of the presence of
continuous plant growth throughout the year and because of spatial and seasonal
variability in nitrogen and phosphorous limitation. Examples of lagoons with such
characteristics are Patos 1. and Araruama L., as well as Ebrie in Ivory Coast. Thus, in
comparing systems, chlorophyll a remains the only useful, practical, and simple measure of TS ranking (Golterman and Gude 1991).
Based on the mean annual chlorophyll stock (Table 3-3), the TS-ranking system (Rast
and Holland 1988) indicates that Flora L., Urussanga 1., Guarapina 1., Barra 1.,
Maric:! 1., Marapendi 1., and Concei<;:ao 1. are eutrophic and that Itaipu 1., CananeiaIguape 1., and the Patos 1. Estuary are mesotrophic. Hypertrophism is found in
Piratininga 1. and oligotrophism in Araruama 1. In Araruama 1. and the Patos 1. Estuary, some portions of the lagoons attain higher trophic states during parts of the
59
calculated by Pick's first law from pore water collected using the in situ "Peeper" sampling technique (Fernex et al. 1992) and applying standard temperature-corrected
diffusion coefficients. The results reflect seasonal variability of benthic nutrient fluxes,
with the highest flux usually occurring during the summer when the primary production is enhanced. Assuming the Redfield ratio to establish the nutrient demand by
phytoplankton primary production, the benthic supply of ammonia and orthophosphate sustains 10-30% of the primary production in the phytoplankton-based coastal
lagoons on both a seasonal and annual basis. In the case of Araruama 1., however,
the microphytobenthos-based primary production was entirely sustained by ammonia and orthophosphate release in winter. In late summer, ammonia was preferentially released over orthophosphate, which covered only 5% of the demand by phytoplankton.
Considering that the relation between sediment oxygen consumption and pelagic
primary production was 30-55% in the Brazilian lagoons, the pelagic compartment
regenerates a somewhat higher fraction of nutrients than the benthic compartment.
Some of the benthic oxygen consumption includes chemical oxygen demand, at least
for the oxidation of sulfide to sulfate. Most of the lagoon sediments are anoxic a few
centimetres below the surface.
3.14
Trophic State
The trophic state (TS), or degree of nourishment of coastal lagoons, is an indicator
that can be used to as a first step to assess the process of eutrophication and also to
develop management policies. There are many available methods for TS ranking
(Lambou et al. 1983).
The simplest measure of TS-ranking is the average annual stock, or peak value, of
chlorophyll a, total nitrogen (TN), and/or total phosphorous (TP). The choice depends
on which nutrient is limiting for primary production and thus should be selected (Rast
and Holland 1988). However, the extrapolation of the trophic state concept, which was
originally developed for phosphorous-limited temperate lakes (Vollenweider 1968;
Vollenweider and Kerekes 1982), presents problems when applied to nitrogen-limited,
tidally dominated estuaries (Rast and Holland 1988; Vollenweider 1992). For example,
using nitrogen as the TS indicator requires information on denitrification because it
has a compensatory effect on eutrophication (Golterman and Gude 1991).
Complications may arise in tropical coastal lagoons because of the presence of
continuous plant growth throughout the year and because of spatial and seasonal
variability in nitrogen and phosphorous limitation. Examples of lagoons with such
characteristics are Patos 1. and Araruama L., as well as Ebrie in Ivory Coast. Thus, in
comparing systems, chlorophyll a remains the only useful, practical, and simple measure of TS ranking (Golterman and Gude 1991).
Based on the mean annual chlorophyll stock (Table 3-3), the TS-ranking system (Rast
and Holland 1988) indicates that Flora L., Urussanga 1., Guarapina 1., Barra 1.,
Maric:! 1., Marapendi 1., and Concei<;:ao 1. are eutrophic and that Itaipu 1., CananeiaIguape 1., and the Patos 1. Estuary are mesotrophic. Hypertrophism is found in
Piratininga 1. and oligotrophism in Araruama 1. In Araruama 1. and the Patos 1. Estuary, some portions of the lagoons attain higher trophic states during parts of the